1. Field of the Invention
The present invention relates to compressors employed in vehicle air conditioners, and more particularly, to compressors that produce little vibration and operate quietly.
2. Description of the Related Art
FIG. 15 shows a typical compressor 200 employed in a vehicle air conditioner. The compressor 200 is a swash plate type and is connected to an engine E by an electromagnetic clutch 210 attached to the front side of the compressor 200.
The compressor 200 includes a housing 201. A crank chamber 202 is defined in the housing 201. A drive shaft 203 is rotatably supported in the housing 201. A swash plate 204 is fixed to the drive shaft 203 and rotates integrally with the shaft 203. A plurality of cylinder bores 206 extend parallel to and about the drive shaft 203 in a cylinder block 205, which constitutes part of the housing 201. A piston 207 is located in each cylinder bore 206. The pistons 207 are connected to the swash plate 204. Valve plates 208 are provided on the front and rear ends of the cylinder block 205. A compression chamber 209 is defined in each cylinder bore 206 between an end of each piston 207 and one of the valve plates 208.
Rotation of the swash plate 204 is converted to linear reciprocation of each piston 207. This compresses refrigerant gas in each compression chamber 209.
The clutch 210 is connected to the front end of the compressor 200 with a bearing 216 in between. The clutch 210 includes an inner hub 214 secured to the front end of the drive shaft 203, an armature 213 secured to the inner hub 214, a pulley 212 and a solenoid 215 for attracting the armature 213 toward the pulley 212. The clutch 210 selectively connects and disconnects the compressor 200 with the engine E in accordance with the cooling load of an external refrigerant circuit (not shown). Exciting the solenoid 215 allows the armature 213 to be coupled to the pulley 212. This transmits the driving force of the engine E to the drive shaft 203 by way of the belt 211, the pulley 212, the armature 213 and the inner hub 214.
The compression stroke of each piston 107 produces a compression reactive force. The compression reactive force is transmitted to the drive shaft 203 through the swash plate 204 and creates torsion between the shaft 203 and the inner hub 214. This creates torsional vibration in the drive shaft 203. The torsional vibration represents torque fluctuation of the shaft 203 and fluctuation of rotational speed (rotational speed fluctuation) of the pulley 212. The torsional vibration also produces resonance in other auxiliary devices that are connected to the compressor 200 by the belt 211. This increases noise in the passenger compartment of the vehicle.
When the compressor reaches certain speeds, torsional vibration of the shaft 203 abruptly increases the torque of the drive shaft 203. The sudden increase in the torque causes the pulley 212 to slip on the armature 213. This suddenly disconnects the transmission of force from the engine E to the shaft 203. The contacting force between the armature 213 and the pulley 212 therefore needs to be great enough to prevent the slipping. This requires that the size of the solenoid 215 be enlarged.
Japanese Unexamined Patent Publication No. 55-20908 describes an electromagnetic clutch that solves the above problems. As shown in FIG. 14, an electromagnetic clutch 220 includes a pulley 225, a solenoid (not shown), an armature 221, a damper 222, a connecting plate 223, a cover 224 secured to a drive shaft 229 and a plurality of springs 228. The armature 221 is secured to the connecting plate 223 with the damper 222 located in between. Exciting the solenoid couples the pulley 225 to the armature 221. The cover 224 is secured to an end of the drive shaft 229. The cover 224 and the connecting plate 223 contact and are urged toward each other by the force of the springs 228. The shape of the cover 224 and the plate 223 allows relative rotation to a certain extent. The relative rotation is converted to reciprocating motion of the connecting plate 223. The reciprocation of the plate 223 is then absorbed by the damper 222. When the armature 221 is coupled to the pulley 225, the force of the engine E is transmitted to the drive shaft 229 through the parts 225, 221, 222, 223 and 224. When an abrupt torsional vibration is generated on the drive shaft 229, the cover 224 and the connecting plate 223 rotate with respect to each other, thereby reciprocating the connecting plate 223. The reciprocation of the connecting plate 223 is absorbed by the damper 222. In this manner the torsional vibration is dampened by the damper 222.
The mechanism for reducing torsional vibration is provided in the path of the torque transmission from the pulley 225 to the drive shaft 229. This arrangement complicates the shape of the connecting plate 223 and the cover 224. Further, the springs 228 must be provided for coupling the plate 223 to the cover 224. The structure of the clutch 220 therefore complicates the manufacture of each part and increases the number of parts.